Burn-in attachment for maintaining rotary furnace hearths



March 24; 1959 R. E. BUCKHQLDT BURN- IN ATTACHMENT FOR MAINTAININGROTARY FURNACE HEARTHS Filed March 15, 1956 2 Sheets-Sheet l I-NVENTORROBERT E. BucKHow'r A'ITRNEY March 24, 1959 R. E. BUCKHOLDT BURN-INATTACHMENT FOR MAINTAINING ROTARY FURNACE HEARTHS 2 Sheets-Sheet 2 FiledMarch 15, 1956 INVENTOR QE RT E. Eve/{How} ATTORNEY United States PatentBURN-IN ATTACHMENT FOR MAINTAINING ROTARY FURNACE HEARTHS' Robert E.Buckholdt, Salem, Ohio, assignor to Edgar Homer Kendall ApplicationMarch 15, 1956, Serial No. 571,823

2 Claims. (Cl. 263-28) This invention relates to the furnace art andmore particularly to improved apparatus for establishing and maintainingprepared load-bearing surfaces on movable hearths in heating furnaces ofthe kind used to heat metal billets, for example, prior to forming androlling operations. Because of the substantially high temperaturesnormally required in such furnaces and the necessity of protecting thesupporting structure of the hearth from such high temx therebyincreasing its load-bearing potential at lower temperatures whileproviding a refractory layer for heat insulation purposes.

Although the resulting chrome ore hearth has been found very desirableand advantageous in the furnace art, being generally accepted; its useand preparation does give rise to several perplexing problems which haveheretofore been unsolved by the prior art. Although the burn-intemperature required for the chrome ore is far above that requiredduring normal heating operations in the furnace, the common prior artpractice has been to utilize the heating furnace proper for the burn-inprocess. When burning-in a new charge of chrome ore on the hearth, thefurnace must therefore be overheated for sustained periods of time,causing scoring and damage to the insulating material of the heatingchamber. This damage requires the rebuilding of the furnace chamber moreoften, thus resulting in increased cost of operation. Also, to securethe required higher temperature potential in the furnace, larger andmore costly burners and other auxiliary equipment are required.

It is therefore the primary object of this invention to provide improvedapparatus for burning-in chrome ore hearth tops in movable hearthfurnaces directly in the furnace proper without overheating the entirefurnace assembly and subjecting the various parts thereof to theelevated temperatures required for the burning-in process. In carryingout the above stated object I provide an assembly which is adapted tofit in the furnace in a direction transverse to the movement of thehearth and which has a plurality of downwardly directed high thermalrelease burners aligned above the chrome ore top of the hearth.

When the attachment is energized the newly added chrome ore on thehearth directly thereunder is heated to the elevated temperaturesrequired for a desired period of time and then another section of thehearth is moved under the burners for proper heating. In this manner theentire surface of the chrome ore may be heated in successive steps toobtain the desired hearth condition.

Another object of the invention is the provision of a Patented Mar. 24,1959 2 burn-in attachment unit which may be adapted for use with hearthfurnaces already in use to prepare the chrome ore. It is contemplatedthat the furnace assembly will not have to be modified in anyappreciable way in accomplishing this objective.

While the applicability of this invention is not necessarily limited torotary hearth furnaces, it is particularly advantageous for such usesince the hearths in such furnaces must necessarily be assembled andbuilt up directly in the annular heating chamber of the furnacestructure and, of course, is not removable therefrom. Thus, if theintended service of such furnace is such as to require a burned-inhearth surface, such burning-in must take place directly in the furnacechamber, requiring the furnace to be operated, during the burning-inperiod, at temperatures considerably higher then normal operatingtemperatures;

These, as well as other objects and advantages of the invention willbecome apparent upon consideration of the following detailedspecification and accompanying drawing wherein there is specificallydisclosed apparatus for burning-in chrome ore hearth tops in movablehearth furnaces constructed in accordance with my invention.

In the drawing:

Figure 1 is a plan view of a rotary furnace utilizing the burn-inattachment constructed in accordance with the teachings of my invention;

Figure 2 is a vertical section taken along the sectional line 11--11 ofFigure 1;

Figure 3 is a partially cut away side view of the burner attachment usedin the furnace; and

- section line IV'IV of Figure 3.

Referring now to the drawing, and initially to Figure 1 thereof, thereis shown a plan view of a rotary hearth furnace, designated generally bythe numeral 10, having a chrome ore topped hearth and utilizing theburn-in attachment 41 of this invention. According to well knownconstruction in the furnace art, the furnace 10 is circular inplan-having a cylindrical inner side wall 11, a similar outer side wall12, and an annularly-shaped roof spanning the concentric side walls.Positioned within the side walls 11 and 12 is the annular hearthassembly 14 suitably supported for rotative movement about its owncenter which center is coincident with the centers of the side walls 11and 12. Adjacent openings 15 and 16 are provided in the outer sidefurnace wall 12 to allow the metal objects to be heated to be moved intoand out of the furnace, respectively.

Now referring to Figure 2 of the drawing, the rotary furnace 10 is builtup between two concentric series of buckstays 17 the function of whichis to provide vertical and lateral support for the side Walls 11 and 12.A circular channel 18 is secured to the inner surface of the outer ringof buckstays 17 and this, together with the multiplicity of circularlyand vertically arranged members 19, supports the side walls of thefurnace 10. The furnace hearth assembly 14 is preferably constructed ofhard refractory brick leaving a circular recess 20 in the top surfacethereof which is filled with chrome ore-21 prepared in a manner to behereinafter more fully de scribed to form the load-supporting hearth ofthe furnace.

, The hearth assembly 14 is supported on a suitable structural steelplatform 22, the latter being carried by a number of wheels 2324traveling on the rail circles 25-26. Rails 25-26 are supported on asuitable framework 27, the latter as well as the entire furnaceassembly, being supported on a concrete base 28. Suitable mechanism (notshown) is employed to rotate the hearth assembly 14 within the furnaceat the controlled rate of speed and to start and stop such rotation. I 1

Evenly spaced about the entire periphery of both the.

inner' and outer side walls 11 and 12, respectively,.are

the fuel burners 29 for burning gaseous fuels to elevate the furnacechamber to the desired temperatures for heating metal objects. The fueland compressed air necessary for elficient combustion is suppliedthrough the circular conduits 30 and 31, respectively, carried adjacentthe rings of buckstays 17 on the supports 32. Suitable means forconnecting the individual burners 29 to the conduits 30 and 31 (notshown) are provided.

To properly exhaust the fumes from the furnace, the passageways 33 whichopen in a space within the furnace and which communicate with theconcentric manifolds 34 positioned directly above the side walls 11 and12 are provided. As indicated in Figure l, the manifolds 34 areconnected through conduit 35 and a power driven exhausting fan 36 to thestack 37.

The hearth assembly 14 is sealed from below by sand seals which consistof quantities of sand in the circular channels 38 and the cylindricallyformed plates 39, the lower ends of which extend down into the sandcarried by channel 38. Plates 39 are secured to the sides of the hearthassembly 14 and inasmuch as they are circularly concentric with thechannels the seals are effectively maintained even during travel of thehearth assembly.

The above construction is well known in the furnace art to be anexpedient heating furnace. Metal objects to be heated are loaded throughthe opening 15 onto the chrome ore hearth 21 and the hearth assembly 14is rotated at the desired speed to allow the objects to obtain thecorrect temperature due to the heat liberated from the burners 29. Afterthe hearth assembly 14 has traveled in a complete circle the heatedobjects are removed through the opening 16 and may be delivered forfurther operations to other apparatus, not shown. It is contemplatedthat vertically slidable doors 40 on the outer ring of the buckstays 17will be closed when the loading and unloading of the furnace has beencompleted to prevent the loss of heat.

As indicated in the previous discussion the preparing of the chrome orehearth in such a furnace as described above presents various andobjectionable problems. To overcome these undesirable features I providea new and novel burn-in attachment for the furnace 10 designatedgenerally by the reference numeral 41. As shown in Figure 2, the burn-inattachment 41 is adapted to fit through the loading opening 15 andextend transversely across the hearth assembly 14 so that when thehearth is rotated about its axis the entire chrome ore hearth 21 iscaused to pass under it. To support the burn-in assembly 41 I provide ashoulder 42 on the inner furnace'wall 11 directly opposite the opening15 which one end of the burn-in attachment rests on while the other endis supported by a suitable removable brick support 43 on the lower sillof the charging opening 15.

In Figures 3 and 4 of the drawing the burn-in attachment'41 is shown toconsist of the rectangular structural steel frame 44 being of suchlength to extend between the side walls 11 and 12 of the rotary furnace10. An inverted U-shaped jacket 45 forms the sides and top of theburn-in unit and is secured by the angles 46 to the structural frame 44.The top and sides 45 not only serve to add rigidity to the burn-inattachment structure but also are adapted to carry suitable means, suchas the tubes 56, for circulating cooling fluid in the jacket 45'whichprecludes the need of refractory or insulating lining on the top andside walls of the assembly and further protects the heating chamber ofthe furnace as will be hereinafter more fully described.

The structural frame 44 also serves as a support for the plurality ofaligned burners 47 directed downwardly toward the-hearth assembly 14.The burners 47 are surrounded by the solid refractory fire brickpartition 48 which-is attached to the frame 44 and extends below theburners. Circular recesses are provided in the firebrick 48 therebyforming burner ports '49 through which the nozzles "50 f =the=-burners"47 "protrude. As is common practice, the burner ports 49 increase incross sectional area in the direction of flame propagation. It iscontemplated that the burners 47 will be of the high thermal releasetype and in the illustrated embodiment these are depicted as utilzingfuel supplied through the conduit 51 while compressed air, necessary foreflicient combustion, is carried in the conduit 52. These conduits 51and 52, run the length of the burn-in attachment 41 and are -surroundedon three sides by the jacket 45. Suitable conduits 53 and 54, made fromstandard pipe fittings, are tapped into the air and fuel conduits 51 and52, respectively, and are provided to communicate and deliver the fueland compressed air to the burners 47. It is understood, of course, thatthe conduits 51 and 52 are connected to adequate supplies of fuel andair (not shown) by suitable means.

In the operation of the burn-in attachment 41 for preparing andburning-in the chrome ore hearth of a rotary furnace, it is assumed thatthe pulverulent chrome ore has been added to the hearth where a newrefractory surface is desired. After this preparatory operation theburn-in attachment 41 is pushed through the opening 15 until one endthereof rests on the shoulder 42 and the other end is supported by thefire brick block 43 on the sill of the charging opening. At this timethe fuel and air supply conduits 51 and 52 are connected to theirrespective sources as well as the water jacket conduits to the supply ofcoolant.

The main furnace chamber is then heated to the maximum temperatureencountered in heating metal workpieces passing through the furnace andafter an interval of time the chrome ore will have obtained thistemperature although no transformation will have taken place as thesetemperatures are usually not high enough to bring about the desiredcondition in the chrome ore. When the ore has obtained thesetemperatures the burnin unit burners 47 are ignited and due to theirpositioning directly above the hearth, the configuration of the ports 49and the refractory fire brick 48, the heat liberated therefrom isdirected and deflected downwardly on a portion of the pre-heated chromeore. The burners 47 are of the high thermal release type and areoperative to give off enough heat to complete the high temperaturetransformation of the chrome ore hearth. As one section of the hearthobtains the desired condition of a hard refractory surface, the hearthassembly 14 may be rotated to bring another portion of the chrome oreunder the burners for the burning-in process, this series of operationsbeing continually repeated until all of the desired chrome ore has beentransformed.

As an example, a rotary furnace installation might be used for heatingmetal blanks prior to further forming operations to a temperature of2400 degrees Fahrenheit while chromie ore requires a temperature of 2700minimum degrees Fahrenheit for the sintering process to take place. Inthis instance, the main heating chamber would be brought to atemperature of 2400 degrees and the attachment operated to raise thetemperature of the chrome ore directly thereunder to that required toobtain the desired conditions.

In order to protect the structural frame of the attachment, as well asthe body portion of the burners 47 and the conduits 51 and 52, coolantis circulated through the tubes 56 thereby substantially isolating thesemembers from the intense heat.

When the entire hearth has been prepared, or a particular portionthereof as desired, the attachment 41 may be retracted and the furnaceis ready to resume normal operations of heating metal workpieces. Itshould be understood, however, that it is possible, and sometimespreferable, to construct the burn-in attachment as an integral part ofthe furnace and this can be accomplished by providing a separate openingin the side wall .12 instead of utilizing the loading or unloadingopenings 15 and 16 with the attachment unit supported above the hearthfar enough to allow headroom for passage of metal objects through thefurnace. In this manner the operation cf initially positioning andretracting the burn-in attachment each time it is needed is precluded.It may also be desirable to position the burn-in furnace between theloading and unloading entrances to the furnace thus separating them by asmall distance and also making it possible to burn-in the chrome orewhile the furnace is still being used to carry metal objects in acontinuous manner through the heating chamber. The burning-in takesplace in this case at a position where there is nothing on the hearthbut the rest of it may be utilized for carrying metal workpieces. Thistype of installation is particularly attractive for use with a hearthwhere the furnace installation is an integral part of a process line andit is undesirable to stop production for burning-in the chrome orehearth.

It should thus be apparent that I have accomplished the objectsinitially set forth by providing improved apparatus for burning-inchrome ore hearth tops in movable hearth furnaces directly in thefurnace proper without overheating the entire furnace assembly. Theinvention teaches means for applying the desired temperature potentialto a relatively small portion of the hearth, thus reducing the number orsize of the burners employed in the main heating chamber.

It is further observed that although this apparatus is especially usefulin the rotary type furnace or other furnaces where the hearth may not beremoved from the main heating chamber, that the apparatus may beemployed in any furnace structure having a movable hearth.

Another important feature of the invention is the pro vision that theburn-in attachment is adaptable for use with furnaces already inoperation with only minor alternations and modifications to the furnaceassembly. A shoulder must be built on the inner wall of the furnace and,depending upon the type of operation desired, an opening provided in theouter wall between the loading and unloading doors. 1

Although I have accomplished the objects initially set forth anddescribed a specific embodiment of my invention, it should be understoodthat certain changes may be made therein without departing from thescope or intent of the invention and reference should therefore be hadto the following appended claims in determining the complete coverage ofthe invention.

I claim:

1. In a combination a rotary furnace having concentric inner and outerspaced side walls, an annular roof joining said side walls, an annularhearth having a refractory upper load bearing surface received betweensaid spaced side walls, means to move said annular hearth, said sidewalls, roof and hearth defining an annular heating chamber, a pluralityof fuel burners disposed along said side Walls of said heating chamberfor heating said chamber during normal operations thereof, at least oneopening in said outer spaced side wall for providing access to saidheating chamber, a burn-in attachment for preparing and maintaining saidrefractory surface of said hearth, said burn-in attachment having anelongated rectangular structural framework, a layer of heat insulatingrefractory material attached to and depending from said framework, saidlayer having a plurality of burner ports therein, a plurality of highthermal release burners mounted from and along the length of saidframework with the nozzles thereof protruding through said ports, a fuelconduit positioned above and extending the length of said framework, aplurality of individual conduits connecting said fuel conduit and saidlast mentioned burners, said burn-in attachment benig removably receivedwithin said opening in said outer side wall and extending in spanningrelation between said inner and outer side walls across said movablehearth, said inner wall having a ledge thereon opposite said opening andsupporting the end of said attachment, and said burner ports and highthermal release burners being closely adjacent said refractory surfaceof said annular hearth for heating that portion of said refractorysurface directly thereunder to a desired degree higher than the normaloperating temperatures of said furnace without overheating the entireheating chamber.

2. In combination a furnace having spaced side walls, a roof joiningsaid spaced side walls, a hearth having a refractory load bearingsurface received between said spaced side Walls, means to move saidhearth, said side Walls, roof and hearth defining a heating chamber, aplurality of fuel burners disposed along said side walls of said heatingchamber for heating said chamber during normal operations thereof, anopening in one of said side walls for providing access into said heatingchamber, a burn-in attachment for preparing and maintaining saidrefractory surface of said hearth, said burnin attachment having anelongated structural framework, 2. layer of heat insulating refractorymaterial attached to and depending from said framework, a plurality ofhigh thermal release burners mounted from and along the length of saidframework with the nozzles thereof protruding through said layer, a fuelconduit positioned above and extending the length of said structuralframework, a plurality of individual conduits connecting said fuelconduit with said last mentioned burners, an elongated jacket ofU-shaped cross section having its ends attached to and generallycoextensive with said elongated structural framework, said jacket andsaid framework defining an enclosed hollow portion above said layer,said fuel conduit being mounted within said hollow portion, means tocirculate coolant within said hollow portion, said burn-in attachmentbeing removably received within said opening is said one of said sidewalls and extending in spanning relation across said hearth, the otherside wall having a ledge thereon opposite said opening for supportingthe end of said burn-in attachment, and said high thermal releaseburners being closely adjacent said hearth for heating that portionthereof directly thereunder to a desired degree appreciably higher thanthe normal operating temperatures of said furnace without overheatingthe entire heating chamber.

References Cited in the file of this patent UNITED STATES PATENTS

